Uncontrolled weeds in crop fields may use nutrients and water needed by crop plants, may shade or choke crop plants, may contaminate crop products with noxious or otherwise undesirable weed seed or other parts of weed plants, and may damage harvesting equipment. Weeds in residential lawns and in recreational and commercial areas such as parks, golf courses, and playgrounds are generally unsightly and detract from appearance in addition to interfering with desired plants and activities. Some weeds in pastures may be toxic to livestock or create other undesirable problems, such as cockleburs or briars. Some weeds also release chemicals into soil that interfere with germination or growth of desired seeds. Seeds of weed plants may be introduced into a field or other region via droppings of birds or other animals or via wind or water in addition to being released from weed plants already growing in the field. Some weed seed may also enter via a crop seed mixture.
Numerous strategies, equipment, and chemicals for dealing with weeds have been developed over the years. Conventional weed control strategies include use of pre-emergence chemical herbicides to prevent germination or initial growth of seedlings, mechanical damage to weed plants via manual or machine cultivation, use of chemical herbicides that enter weed plants via absorption through leaves or other plant structures and interfere with weed plant growth, and convective or radiant heating of weeds via combustion of kerosene, propane, or other combustible fuels. Each such approach has its advantages and drawbacks. Mechanical cultivation, whether by machine or by hand tools, frequently results in damage to desired plants directly or through disturbance of soil and roots therein. Manual cultivation via hoe or other hand tools is generally difficult and uncomfortable labor and frequently subjects field laborers to back, muscular, and other pain both during and after performing such work. Manual and other mechanical cultivation also increases loss of valuable topsoil through rain and wind erosion. Heating of weeds using conventional combustion techniques generally involves use of increasingly expensive carbon-based fuels and also contributes to release of carbon dioxide to the atmosphere with potential implications for global warming or other climate changes. Direct heating via open flame is also difficult to control and may thus result in damage to or stunting of desired plants, particularly in large scale applications. Chemical herbicides may also cause damage to desired plants via over-spray or wind drift, and herbicide contaminated rainfall runoff from treated fields and lawns may also cause undesirable effects on downstream flora and fauna, particularly on aquatic or amphibian animals, as well as rural or municipal water supplies. Techniques, sensors, and equipment have been developed to provide more selective or controlled precision application of chemical herbicides, including techniques for variable rate applications of chemical herbicides responsive to weed concentrations detected and mapped via use of overhead sensor systems (e.g., on aircraft or satellites), and spot spraying of herbicides onto specific or individual weed plants using information from ground-equipment-mounted sensors that detect and/or identify individual weed plants. Although much has been done to enhance selectivity, provide rapid breakdown, and otherwise reduce undesirable environmental and ecological effects of chemical herbicides, there is continuing and even increasing concern among environmentalists, ecologists and others about the long term effects on agricultural sustainability and society as a whole of continued or expanding use of chemical herbicides. Various studies have indicated increased incidence of certain diseases or health conditions among agricultural workers regularly exposed to such chemicals. Residues from herbicides, insecticides, and other agricultural chemicals are found in harvested fruits, vegetables, and other crop products as well as in ponds, streams, rivers, and in fish harvested therefrom. Residues from agricultural chemicals are even found in subterranean aquifers as well as rural or municipal water supplies. Some studies have indicated increased incidence of certain diseases or other abnormalities even in non-farming populations exposed to such residues. Concern about potential health implications of residues of agricultural chemicals have led many consumers to be attracted to so-called “organic” or “natural” produce and other agricultural products grown without use of chemical pesticides (i.e., insecticides, herbicides, and fungicides).
To reduce or eliminate impacts of chemical herbicides on crop plants, some crop plants have been “genetically engineered” to tolerate exposure to selected herbicides without significant damage. However, some environmentalists and others fear that development of crops genetically modified to resist selected herbicides will generally lead to increased use of the selected herbicides that may now be sprayed over an entire crop field rather than being applied in a more controlled fashion. There are concerns among environmentalists, conservationists, and within USDA about the long term effects and sustainability of such practices, including effects of current and future herbicides on essential microbes and other micro-organisms in crop soils, potential development of herbicide resistance in weeds via natural selection or via migration of genes from genetically modified crop plants which confer tolerance to selected herbicides, and effects of runoff into surrounding environments, including ponds, lakes, streams, and subsurface water. Consequently, there is a strong push even in conventional as well as organic crop production for using “sustainable” agricultural practices that reduce use of chemicals that may cause damage to crop fields and the environment as a result of long-term use.
Some researchers and lay persons have suggested potential use of concentrated solar energy for damaging weeds, but have not described the controls, safety measures, and other features needed to provide practical, safe, and convenient use of solar energy for weed control. Some researchers have investigated use of concentrated solar energy to damage seed and seedlings but were apparently pursuing concepts for apparatus that could be towed with conventional tractors. The use of such tractors introduces additional costs over the instant invention presented herein due to the requirements for operators and conventional fuel. Furthermore, the slow speed which will generally be needed to provide sufficient exposure of weed plants may not be efficient use of tractor equipment designed to pull significant loads at moderate speeds. Additionally, the heavy weight of conventional tractors may also preclude use of such equipment in wet fields at the revisit intervals needed for effective control of emerging weed plants. Typically, weeds emerge rapidly following significant rainfall which may also render fields inaccessible to conventional equipment during the period of most rapid weed emergence. Thus, when using conventional tractors, access for weed control may be limited at the time when the need for exposure and control of emerging weed seedlings with concentrated solar energy is greatest.
On a different front, instability in price and availability of foreign oil places additional strains and uncertainties on farmers and park and lawn maintenance personnel relative to fuel resources needed to apply herbicides via tractor spray rigs or via conventional aerial application of herbicides (e.g., using “crop duster” aircraft). Many of the conventional weed control techniques and equipment for use in crop production are centered around use of a conventional tractor using conventional carbon-based “fossil” fuels for propulsion within crop fields. Tractors must generally be relatively heavy and use tires with high-traction features for their normal role of towing plows or other equipment. Concerns about burning fossil fuels and contributing to carbon dioxide concentrations in the atmosphere are also driving a need for alternatives that do not require use of fossil-fuel burning internal combustion engines for chemical applications, cultivation, or other means of weed control.
Precision herbicide application devices, e.g., for tractor spray booms, that use sensors to detect weeds in row middles and then make “spot treatment” applications of herbicides, have been available for a number of years. However, these devices are expensive to buy and costly to maintain due partly to collection of spray mist, and dust created by tractor movement, on optical lens and other components of such devices. Furthermore, these devices still use herbicides and may require dedicated use of fuel resources for tractors when weed control is needed independent of other crop production activities. Furthermore, some fields may be inaccessible for extended periods due to rain causing tractors and other equipment carrying heavy chemical and fuel loads to sink into wet, muddy areas in a field, lose traction, or accumulate sticky mud (“gumbo”) on conventional tires or treads of tractors and other equipment. In addition, some field areas may be inaccessible to conventional tractors or other heavy ground equipment once irrigation pipes have been installed.
Residential, commercial, and recreational lawns are frequently subjected to comprehensive treatment programs involving pre-emergence herbicides as well as herbicides applied during a growing season. Runoff and permeation of chemicals from such treatments contribute to the chemical contamination of surface and subterranean water supplies.
An object of the instant invention is to provide methods and apparatus to help control weeds in crops, residential and commercial lawns, and in other areas, generally using only solar energy, concentrated to provide a weed damage mechanism, and also, in some embodiments, using solar energy to provide power for propulsion, sensors, and other functions, and thus generally not require use of chemical herbicides or use of conventional fossil fuels for a weed damage mechanism (e.g., via flame heating) or for propulsion of machinery used for weed control.
Another object of the instant invention is to provide cost-effective weed control using concentrated solar energy as the principal weed plant damage mechanism without contaminating agricultural workers, consumers, and the environment with chemical herbicides.
It is another object of the instant invention to provide embodiments of apparatus for implementing effective weed control on different scales including residential weed control, weed control in small organic plots, and weed control in large scale farming operations such as in the Mississippi Delta or in Central Valley, Calif.
Objectives of the instant invention include describing apparatus and embodiments to implement various weed control strategies at various scales ranging from manual, human operated to highly-automated and autonomous robotic systems that can work unattended for extended durations in assigned fields or other locations. Some applications and/or embodiments may use a concentrated, collimated beam, and other applications and/or embodiments may use a converging beam for different applications, or to selectively protect objects beyond a focused spot, where such beam diverges and intensity is reduced. A collimated beam may be used to provide a concentrated intensity level over a broader area (e.g., a spot 0.5 to 2 inches in diameter) which is sufficient to rapidly heat a leaf to a damaging temperature with less risk of starting a fire than might exist if a more highly focused beam comes in contact with a combustible material or heats a surface to a temperature that can ignite a combustible material.
It is another object of the instant invention to provide an apparatus whereby manual control of weeds may be realized with less need for stooping, kneeling, bending over, or using a hoc, thereby reducing fatigue and pain experienced by agricultural and lawn care laborers as well as residential homeowners.
It is another object of the instant invention to provide methods and apparatus for implementing alternative weed control strategies which, in some crops and applications, may emphasize kill of all non-crop or non-desired plants in a field or lawn, and which, in other crops or applications, may tolerate some weed growth but simply emphasize damaging growth terminals of weed plants and/or tendrils to prevent weeds from growing above a certain height so that they will be largely shaded by crop plants as a crop matures and/or achieves “canopy closure” (i.e., where the combination of row spacing and crop plant development substantially reduces the amount of direct sunlight reaching areas below the leaves of crop plants, thereby starving germinating or low growing weed plants of sunlight). In view of environmental concerns and need for sustainable agricultural and societal practices, weed control strategies may be different for different crops and applications, and may also be changed as a function of crop maturity, time in a growing season, and drought or other environmental conditions. Similarly, different damage mechanisms may be selected for different growth sizes and/or types of weeds. For example, some vines have been found to be particularly susceptible to damage to their leaves by using solar energy concentrated, typically in a broader spot (as from a circular lens) or line (as from a cylindrical lens), only to an intensity that provides rapid heating of leaves to temperatures in a range from around 150 degrees Fahrenheit up to a few hundred degrees, thereby causing significant damage and breakdown to cells and photosynthesis and nutrient transport structures within the leaves. For some other weed plants, it may be more efficient and/or more effective to use solar energy concentrated to a higher intensity, typically in a smaller spot, to more rapidly damage selected portions of a plant structure without necessarily attempting to damage the leaves. For example, weeds such as dandelions and others that tend to put out a number of low-laying leaves from a central crown may be more susceptible to more highly concentrated solar energy focused on the central area of the plant where leaf stems joint the root, so that significant localized heating damage to the central area of the plant effectively decouples the leaves from the root, preventing transport of water and soil nutrients to the leaves and transport of critical photosynthate compounds from the leaves to the roots, typically resulting in loss of the leaves and loss of critical nutrients to the root structure. Although the temperature at which cellular damage occurs may still be in a range from approximately 150 degrees to 300 degrees Fahrenheit, the thicker structures of the stems where they join the roots will typically require a higher temperature or extended exposure durations on the exposed sides of the structure so that temperatures of shielded portions of the structure are also sufficiently elevated either via heat conduction or via removal of intervening plant tissue so that essentially all of the stem area is sufficiently damaged to severely impair or prevent its normal nutrient and water transport functions. Although many weed plants are particularly hardy and damage tolerant, and may be able to establish new growth after a few days, repeated treatment of such plants at selected intervals (e.g., every 7 to 10 days) appropriate to different growth rates of different weed plants and environmental conditions (e.g., good rainfall and sunlight or drought conditions) will generally prevent many weed plants from becoming established in a field or lawn. For virtually all weeds, including those that grow from seeds or those which propagate and emerge from root extensions (as in rhizomes), it is generally most desirable to cause damage to newly emerging leaves when they are most susceptible. Early damage to emerging leaves also prevents generation and transport of photosynthate nutrients back to the roots, which will generally be fatal to weed plants newly emerging from seeds, and which will generally at least stunt or impair grown of weeds that propagate via root extension. Thus, to support tradeoffs between conventional use of herbicides and methods and apparatus of the instant invention for weed control, it is generally desirable that the apparatus and methods of the instant invention support frequent and economic re-treatment of crop fields or other areas where weeds are to be controlled. As will be illustrated and described later herein, this need for more frequent re-treatment when using concentrated solar energy as compared to conventional treatment with herbicides or cultivation will generally drive design choices to innovative lighter weight and less expensive vehicles. However, these design trades are readily accommodated by the use of concentrated solar energy requiring typically only lightweight Fresnel lens, or other stepped surface or lightweight conventional lens, or holographic optical elements, or other solar energy concentrating technologies and apparatus, and solar-powered propulsion, so that the burden of carrying the weight of tanks filled with chemical herbicides and fossil fuels is eliminated. By making such vehicles robotic and essentially autonomous, the cost of labor for mixing chemicals and servicing and driving tractors or similar equipment for weed treatment is also avoided or substantially reduced.
Methods and apparatus of the instant invention may be used as a primary method of weed control in some applications, but in other applications and weed control strategies, methods and apparatus of the instant invention may be used as a secondary, backup, or follow-on treatment of weeds in a hybrid strategy combining use of convention control methods with use of methods and apparatus of the instant invention. For example, conventional herbicides or cultivation may be used for initial control of a typically heavy growth of weeds that may be allowed to develop, or even be desirable to prevent soil erosion, over a winter or other period when no crop is being grown in a field. After an initial treatment or mowing controls most of the weeds, methods and apparatus of the instant invention may then be used to control weed seedlings or continued growth or re-emergence of weeds not killed by conventional initial control methods. Similarly, selected capabilities of the instant invention may be used to provide spot treatment capabilities for individual weed plants or patches of weed plants that have developed resistance to, or are not otherwise controlled by, conventional herbicides.
Some embodiments of the instant invention comprise units that may be worn as a backpack by individual laborers to provide a weed control device that may be operated much like a conventional backpack sprayer, but which uses a completely different damage mechanism, namely concentrated solar energy. Other embodiments comprise inexpensive, autonomous, solar powered, robotic, lightweight unmanned ground vehicles and/or lighter-than-air or almost-lighter-than-air, very low altitude (e.g., six feet above ground level) unmanned robotic air vehicles that may employ global positioning system (GPS) and/or Differential GPS systems or other means for navigation and precision location reference, may employ sensors to detect and/or identify weed plants, may use solar photovoltaic cells to provide electric power for propulsion motors, and may use Fresnel lens or other stepped surface lens or holographic optical elements, diffractive optics, binary optics, or other solar energy concentrating techniques and apparatus, and light guides, to collect and deliver concentrated solar energy to damage leaves and other portions of weed plants. For example, such systems may:
(1) use differential GPS navigation to drive or “fly” slowly (e.g., 0.25-5 mph) in a controlled pattern (e.g., down rows) within or just above a crop field,
(2) use RF, laser/optical, and/or ultrasonic/acoustic sensors, and signal and/or image processing technologies, which may include pattern recognition, digital or optical correlation, spectral analysis or spectral intensity ratios (e.g., in some embodiments just detecting green vs brown) to detect non-crop plants (i.e., weeds) in crop fields, and
(3) use concentrated solar energy to damage one or more selected portions of non-crop plants, wherein solar energy may be                (a) collected above a crop and concentrated via a large (e.g., 1 meter) Fresnel lens or an array of smaller Fresnel lens or holographic optical elements, and        (b) delivered to targeted areas of crop plants through (i) an optical train comprising lens and mirrors, (ii) one or more optical fibers, (iii) other optical guides, or (iv) some combination of the above.        
Various embodiments of the instant invention will benefit not only organic farmers, who want to produce products free of chemical contamination, but also conventional farmers who must deal with issues of costs, herbicide resistance, environmental and regulatory implications of agrochemicals, and consumer acceptance of chemically treated or genetically modified crops. Other embodiments will benefit residential or commercial lawn and park owners and/or landscape maintenance personnel concerned about environmental and health implications of use of chemical herbicides. Other beneficiaries include cattle, dairy, and other livestock or livestock product producers concerned about toxic and other effects of weeds on their livestock and hay harvesting equipment but who may also be concerned about exposing livestock to chemical herbicides.
As noted, conventional approaches for pest weed control suffer from risks of resistance development to herbicides in some weed species for which control is desired as well as reduced consumer acceptance of use of agricultural chemicals (e.g., witness increasing market for “organic” and “natural” products produced without chemical pesticides or genetically modified crops). The use in some embodiments of the instant invention of precision sensors and precision targeting of individual weed plants significantly reduces concerns with development of resistance since the energy needed for a desired “kill” or other selected effect can be applied with less concern about collateral damage to non-targeted resources. Some embodiments of the instant invention may be used in conjunction with conventional herbicide applications, wherein methods and apparatus of the instant invention may be used to detect and/or provide a “follow-up” treatment of weeds that have developed a resistance to chemical herbicides.
Targeted areas of weed plants may be selected to attempt to kill a weed plant or to simply induce sufficient damage to growing tips, tendrils, and other key portions of weed plants so that the weeds are kept below the crop canopy or below a level where the weeds could interfere significantly with development, maturation, and harvesting of the crop.